Shaped articles of melamine/formaldehyde foams having low formaldehyde emission

ABSTRACT

Shaped articles of melamine/formaldehyde foam have a formaldehyde emission of less than 0.1 ppm, determined according to DIN 55666, and are obtainable by the following process: a) a foam is prepared from a melamine/formaldehyde precondensate having a molar melamine:formaldehyde ratio greater than 0.5, b) the foam obtained is annealed at below 200° C., and c) the annealed foam is molded in a press at from 160 to 240° C. and an absolute pressure from 5 to 100 bar in the course of from 15 to 120 seconds to give the shaped article.

The present invention relates to shaped articles ofmelamine/formaldehyde foam, which shaped articles have a formaldehydeemission of less than 0.1 ppm, determined according to DIN 55666, andare obtainable by the following process;

-   a) a foam is prepared from a melamine/formaldehyde precondensate    having a molar melamine:formaldehyde ratio greater than 0.5,-   b) the foam obtained is annealed at below 200° C., and-   c) the annealed foam is molded in a press at from 160 to 240° C. and    an absolute pressure of from 5 to 100 bar in the course of from 15    to 120 minutes to give the shaped article,

The present invention furthermore relates to said process for theproduction of the shaped articles, and the use of the shaped articlesfor acoustic and thermal Insulation.

Owing to their material properties, such as high heat resistance,advantageous fire behavior and good resistance to chemicals,three-dimensional moldings of open-cell, resilient, thermosettingplastic foams are particularly suitable for demanding applications Inheat and sound insulation.

Open-cell resilient foams based on melamine/formaldehyde condensates andprocesses for their preparation are known and are described, forexample, in the Patent Applications EP-A 17 671, 17 672 and 37 470 andthe corresponding patents. A blowing agent-containing solution ordispersion of a melamine/formaldehyde precondensate is foamed byheating, for example by means of hot air, steam, exposure tohigh-frequency radiation or exposure to microwave radiation or byutilizing the heat of reaction, to a temperature above the boiling pointof the blowing agent. Depending on the foaming process and molding, afoam block or strand is obtained, which Is cured by annealing (heattreatment in which the foam is kept at a defined, generally elevatedtemperature for a defined time) to give the finished foam.

While simple shaped articles, for example sheets or strips, can beproduced from the foam by cutting or sawing, more demanding shapingmethods are required for shaped articles having a more complicatedthree-dimensional shape. Such parts having a complicated shape are, forexample, contained in motor vehicles (e.g. engine space insulation) ormachines or serve as pipe Insulation. For the production of such parts,FR-A 1 108 336 discloses molding a foam which is In the curing state butstill moldable and subsequently completing the curing of the foam thuscompressed. U.S. Pat. No. 3,504,064 and EP-A 464 490 describe processesin which the foam is treated with water or steam and is molded before orafterward. EP-A 111 860 describes the molding of melamine resin foams atfrom 60 to 300° C. and at least 1.2 bar absolute pressure.

The shaped articles of melamine/formaldehyde resin which are obtained bythe abovementioned processes contain residual amounts of unconvertedformaldehyde which are continuously released into the ambient air over along time. These formaldehyde emissions increase with increasingtemperature and humidity. They are undesirable and, particularly whenthe shaped articles are used In closed rooms, are disadvantageous. Forexample, In Interior rooms of buildings or in a vehicle interior, theformaldehyde concentration of the air should be as low as possible.

WO 01/94436 describes a process for the preparation ofmelamine/formaldehyde foams having a reduced formaldehyde emission, forwhich purpose a melamine/formaldehyde precondensate having a molarmelamine: formaldehyde ratio greater than 1:2 is used. The blowingagent-containing mixture to be foamed is expanded by heating to give,for example, right parallelepiped strands or blocks. Thereafter, theexpanded foam blocks are annealed for from 1 to 180 minutes at from 120to 300° C., in the examples for 30 minutes at 220° C., and are cured.The foams obtained in this manner have a low formaldehyde content butare not thermoformable.

EP-A 451 535 describes a process for the production of a shaped articlefrom melamine resin foam, in which the shaped article blank isimpregnated with a heat-curable binder and then molded at elevatedtemperatures. Binders used are phenol resins or melamine resins, whichare applied to the surface of the blank by spreading or are applied asfoam.

DE-A 196 49 796 discloses a similar process, a (meth)acrylamide polymerdispersion being used as the binder. The two last-mentioned processesaccordingly require an additional starting material which has to beapplied in an additional operation.

The shaped articles obtained by the processes of the prior art withoutImpregnation by pressing, in particular sheet-like shaped articles, donot have the desired geometry in all cases, i.e. the three-dimensionalshape of the finished shaped article deviates from the geometry of thecompression mold and the shaped article does not have the desired shape.Moreover, the borders or edges of the shaped part frequently do not havethe desired stability, for example they are not closed, or do not have asufficient mechanical load capacity. In these cases, the shaped articlecannot be used for applications which require a good accuracy of fit,for example in vehicle construction, or the geometry of the shapedarticle or the edges have to be reworked in an additional complicatedoperation.

It is an object of the present invention to remedy the disadvantagesdescribed. In particular, it is an object of the present invention toprovide shaped articles of melamine/formaldehyde foam which have a lowformaldehyde emission.

It was also Intended to provide a process by means of which the shapedarticles can be produced in a simple manner. For example, the aid ofwater or steam for shaping was to be superfluous.

Furthermore, the shaped articles should be capable of being producedwithout the presence of binders. In particular, the process shouldmanage without the additional impregnation step in which the binder isapplied.

Moreover, the shaped articles should have exactly the desired geometryand stable, precisely shaped borders or edges.

Finally, it was intended to provide shaped articles which meet allabove-mentioned requirements simultaneously, i.e. the shaped articlesshould have a low formaldehyde content and should be capable of beingproduced in a simple manner, in the desired geometry and with stable andprecise borders or edges, in few process steps, without shaping by meansof steam, and without impregnation with binders.

We have found that these objects are achieved by the shaped articles,processes and uses defined at the outset. Preferred embodiments of theinvention are described In the subclaims.

According to the invention, the shaped articles of melamine/formaldehydefoam have a formaldehyde emission of less than 0.1 ppm, determinedaccording to DIN 55666 of April 1995. 0.1 ppm corresponds to 0.12 mg offormaldehyde per m³ of air,

The formaldehyde emission Is preferably less than 0.05 ppm, determinedas described above.

The novel shaped articles accordingly have a particularly lowformaldehyde content. They are obtainable by a novel process containingthree steps a), b) and c).

In step a) of the process, a foam is prepared from amelamine/formaldehyde precondensate having a molar melamine:formaldehyderatio greater than 0.5. This is effected in a manner known per se and isdescribed, for example, in WO 01/94436. Here, a melamine/formaldehydeprecondensate is used as a starting material. Melamine/formaldehydecondensates may contain, in addition to melamine, up to 50, preferablyup to 20, % by weight of modifying compounds and, in addition toformaldehyde, up to 50, preferably up to 20, % by weight of otheraldehydes, in the form of condensed units. An unmodifiedmelamine/formaldehyde condensate is particularly preferred. Examples ofsuitable modifying compounds are alkyl- and aryl-substituted melamine,urea, urethanes, carboxamides, dicyandiamide, guanidine, sulfurylamide,sulfonamides, aliphatic amines, glycols, phenol and derivatives thereof.Other aldehydes which may be used are, for example, acetaldehyde,trimethylolacetaldehyde, acrolein, benzaldehyde, furfurol, glyoxal,glutaraldehyde, phthalaldehyde and terephthalaldehyde. Further detailson melamine/formaldehyde condensates are to be found in Houben-Weyl,Methoden der organischen Chemle, Volume 14/2, 1963, pages 319 to 402.

The molar melamine: formaldehyde ratio is defined as the quotient of theamount of melamine and amount of formaldehyde and, according to theinvention, is greater than 0.5 (i.e, 1:2). It Is preferably from 1 (i.e.1;1) to 0.526 (i.e. 1:1.9), In particular from 0.769 (i.e. 1:1.3) to0.556 (i.e. 1:1.8).

According to EP-A 37470, the melamine resins advantageously containsulfite groups in the form of condensed units, which can be effected,for example, by adding from 1 to 20% by weight of sodium bisulfiteduring the condensation of the resin. It has now been found that arelatively high content of sulfite groups in the case of a constantmelamine: formaldehyde ratio results in a higher formaldehyde emissionof the foam. The precondensate used should therefore preferably containvirtually no sulfite groups, i.e. the content of sulfite groups shouldpreferably be less than 1%, particularly preferably less than 0.1%, inparticular zero, based on the precondensate.

The addition of an emulsifier or of emulsifier mixture is required foremulsifying the blowing agent and for stabilizing the foam. Anionic,cationic and nonionic surfactants and mixtures thereof may be used asthe emulsifier. Suitable anionic surfactants are diphenylene oxidesulfonates, alkane- and alkylbenzenesulfonates,alkylnaphthalenesulfonates, olefinsulfonates, alkylether sulfonates,fatty alcohol sulfates, ether sulfates, alpha-sulfo-fatty esters,acylaminoalkanesulfonates, acylisethionates, alkyl ether carboxylates,N-acylsarcosinates, alkyl and alkyl ether phosphates. Alkylphenolpolyglycol ethers, fatty alcohol polyglycol ethers, fatty acid olyglycolethers, fatty acid alkanolamines, EO/PO block copolymers, amine oxides,lyceryl fatty esters, sorbitan esters and alkylpolyglucosides may beused as nonionic urfactants. Cationic emulsifiers which may be used arealkyltriammonlum salts, alkylbenzyldimethylammonium salts andalkylpyridinium salts. The emulsifiers are preferably added in amountsof from 0.2 to 5% by weight, based on the resin.

In order to produce a foam from the melamine resin solution, saidsolution must contain an emulsified blowing agent, the amount dependingon the desired density of the foam. In principle, both physical andchemical blowing agents may be used in the novel process. Possiblephysical blowing agents are, for example, hydrocarbons, halogenated, inparticular fluorinated, hydrocarbons, alcohols, ethers, ketones andesters In liquid form or air and CO₂ as gases. Examples of suitablechemical blowing agents are isocyanates as a mixture with water, CO₂being liberated as the effecting blowing agent, and furthermorecarbonates and bicarbonates as a mixture with acids, which likewiseproduce CO₂, and azo compounds, such as azodicarboxamide. In a preferredembodiment of the invention, from 1 to 40% by weight, based on theresin, of a physical blowing agent having a boiling point of from 0 to80° C. are added to the aqueous solution or dispersion; In the case ofpentane, it is preferably from 5 to 15% by weight.

Curing agents used are acidic compounds which catalyze the furthercondensation of the melamine resin. The amounts are from 0.01 to 20,preferably from 0.05 to 5, % by weight, based on the resin. Inorganicand organic acids are suitable, for example hydrochloric acid, sulfuricacid, phosphoric acid, nitric acid, formic acid, acetic acid, oxalicacid, toluenesulfonic acids, amidosulfonic acids and acid anhydrides.

Depending on the use of the shaped article, the aqueous solution ordispersion may be free of further additives. For some purposes, however,it may be advantageous to add up to 20, preferably less than 10, % byweight, based on the resin, of conventional additives, such as dyes,flameproofing agents, UV stabilizers, and compositions for reducing thecombustion gas toxicity or for promoting carbonization. Since the foamsare generally open-pore and can absorb water, it may be necessary forsome intended uses to add water repellants in amounts of from 0.2 to 5%by weight. For example, paraffin dispersions, silicone dispersions andfluoroalkane dispersions, in particular emulsions thereof, are suitable.

The concentration of the melamine/formaldehyde precondensate in themixture of precondensate and solvent may vary within wide limits of from55 to 85, preferably from 63 to 80, % by weight. The preferred viscosityof the mixture of precondensate and solvent is from 1 to 3 000,preferably from 5 to 2 000, mPa·s.

The additives are homogeneously mixed with the aqueous solution ordispersion of the melamine resin, it being possible, if necessary, alsoto force in the blowing agent under pressure. However, it is alsopossible to start from a solid, for example spray-dried, melamine resinand then to mix this with an aqueous solution of the emulsifier, thecuring agent and the blowing agent. The mixing with the components canbe carried out, for example, in an extruder. After the mixing, thesolution or dispersion is discharged through a die and immediatelythereafter heated and foamed thereby.

The heating of the blowing agent-containing solution or dispersion canin principle be carried out—as described, inter alia, in EP-A 17671—bymeans of hot air, steam, exposure to high-frequency radiation orexposure to microwave radiation or by utilizing the heat of reaction.Preferably, however, the required heating is carried out by exposure toultrahigh frequency radiation, according to EP-A 37470. In the case ofthis dielectric radiation, it is possible in principle to employmicrowaves in the frequency range from 0.2 to 100 GHz. For industrialpractice, frequencies of 0.915, 2.45 and 5.8 GHz are available, 2.45 GHzbeing particularly preferred. A radiation source of dielectric radiationis the magnetron, it also being possible to effect exposuresimultaneously with a plurality of magnetrons. During the exposure toradiation, it should be ensured that the field distribution is veryhomogeneous. Expediently, the exposure to radiation is carried out insuch a way that the power consumption of the solution or dispersion Isfrom 5 to 200, preferably from 9 to 120, kW, based on 1 kg of water inthe solution or dispersion. If the power consumed is lower, no foamingtakes place and the mixture merely cures. If the procedure is effectedwithin the preferred range, the mixture foams all the more rapidly thegreater the power consumption, Above about 200 kW per kg of water, thefoaming rate no longer increases substantially.

The exposure of the mixture to be foamed to radiation is usuallyeffected immediately after it has emerged from the foam die. The mixturewhich is foaming as a result of a temperature increase and evaporationof the blowing agent is applied, for example, onto revolving belts whichform a rectangular channel for shaping the foam. A foam strand, which isusually divided into slabs, is obtained.

Suitable melamine/formaldehyde foams are commercially available, forexample, as Basotect® from BASF.

In step b) of the novel process, the foam obtained In step a) isannealed at below 200° C. Preferably, annealing Is effected attemperatures (annealing temperatures) above 100° C. The annealingtemperature is preferably from 110 to 200° C., in particular from 110 to160° C.

During the annealing, postcuring takes place, i.e. the foam curesfurther. Moreover, the annealing reduces the formaldehyde emission ofthe foam, Residues of other volatile ingredients are also substantiallyremoved during the annealing, for example monomer residues, blowingagent and other assistants.

The duration of the annealing (annealing time) depends, inter alla, onthe dimensions of the foam, its composition and the temperature at whichannealing is effected. Annealing time and annealing temperature arechosen in the manner known to a person skilled in the art, so that thepostcuring described can take place. The annealing time Is preferablyfrom 5 to 60, in particular from 10 to 30, minutes. The pressure(annealing pressure) prevailing during the annealing may be, forexample, atmospheric pressure (1 013 mbar).

The annealing temperature and pressure may be constant over the entireannealing time or may be varied in a suitable manner. Preferably,constant conditions are employed, but temperature or pressure programsmay also be advantageous.

The annealing can be effected by conventional methods In conventionalapparatuses, for example in heating ovens or heating chambers. However,annealing is preferably effected by means of hot air or other hot gases,which are passed through the foam.

In a particularly preferred embodiment, annealing Is effected directlyafter the preparation of the foam, by treating the foam obtained in thefoam preparation, for example the foam slabs mentioned, with hot air.The hot air flowing through cures the foam slab.

In an embodiment which is likewise preferred, Individual sheets orlayers of, for example, from 0.1 to 10, in particular from 0.5 to 5, cmthickness are produced from the annealed foam slab obtained in thismanner by cutting. If required, a blank can be produced from the sheetor layer obtained, for example by trimming the edges of the sheet orlayer appropriately, or the blank can be punched out of the sheet orlayer. The foam sheet or layer obtained or the blank can then be moldedin step c) of the process.

Of course, suitable foam sheets, layers or blanks can also be producedin another manner, for example by sawing instead of cutting, or by otherconventional finishing methods. It is also possible, but not preferred,to design the foaming and annealing in such a way that a sheet or layerof the desired thickness forms immediately, i.e. without cutting orother finishing.

The foam sheet or layer or the blank preferably has the same thicknesseverywhere (plane-parallel surfaces). Depending on the desired geometryand density distribution of the finished shaped article, however, it isalso possible, for example by appropriate cutting of the foam slab orcontour or profile cutting, also to produce sheets, layers or blankswhich are wedge-shaped or roof-shaped or non-plane-parallel in anothermanner.

It is also possible first to produce foam sheets, layers or blanks fromthe unannealed foam and then to anneal them.

In step c) of the novel process, the annealed foam obtained In step b)is molded in a press at from 160 to 240° C. and an absolute pressure offrom 5 to 100 bar in the course of from 15 to 120 seconds to give theshaped article.

Preferably, molding is carried out at a temperature (press temperature)of from 180 to 220° C. and an absolute pressure (press pressure) of from10 to 80 bar. The preferred press time Is from 20 to 60 seconds.

Press temperatures, pressures and times to be chosen in the individualcase depend in the usual manner on the composition of the foam (forexample the type and amount of the curing agent) and on the density,thickness and hardness of the foam to be molded, for example also afterthe pretreatment of the foam, which also Includes the annealing in stepb). Moreover, inter alia, the density, thickness, form and hardness ofthe desired shaped article, and any laminations or top layers (seebelow) present, have to be taken into account. Press temperature,pressure and time are preferably set in such a way that the shapedarticle obtained in step c) substantially already has the final threedimensional shape.

Shaped articles having a large area or large volume may require a longerpress time than smaller shaped articles. Moreover, the press pressurecan, If required, be all the higher and/or the press time all the longerthe harder or thicker the annealed foam and the higher the desireddensity of the finished shaped article is to be.

Press temperature and press pressure may be constant over the entirepress time or may be varied in a suitable manner. In general, molding iseffected under constant conditions, but temperature or pressure programsmay also be advantageous, particularly in the case of parts which arelarge or have complicated shapes.

The molding Is effected in a conventional manner and preferablybatchwise, by placing the annealed foam obtained in step b), preferablyin the form of a foam sheet, layer or blank, in a suitable press andmolding it. The compression mold Is as a rule heatable, for example byelectric heating or heating by means of a heating medium, and the pressis usually provided with an ejection apparatus. Contour molds, by meansof which those shaped articles which are to have precisely shaped edgesor borders, for example profiled edges or lips, can be particularlyreadily produced are suitable as a compression mold.

Suitable presses are, for example, daylight presses (single- ormulti-daylight presses), toggle presses, down-stroke presses, moldingpresses (transfer molding presses), up-stroke presses and automaticpresses. After the molding, the press is usually opened and the finishedshaped article is removed from the press by means of an ejectionapparatus.

The shaped articles obtainable by the novel process described abovealready have very low formaldehyde emissions of not more than 0.1 ppm,determined as stated above.

In a preferred embodiment, after the molding (step c)), the finishedshaped articles are stored in step d) at a temperature (storagetemperature) of above 180° C. for at least 30 minutes (storage time).

Preferably, the storage temperature is not more than 240° C., andparticularly preferably from 200 to 220° C. Preferably, the shapedarticles are stored at from 30 to 120 minutes. The storage can beeffected, for example, at atmospheric pressure, e.g. 1 013 mbar.

As a result of the subsequent storage, the formaldehyde emission can beeven further reduced. The content of other, abovementioned volatileingredients can also be further reduced. Moreover, it was observed thatthe shaped articles become more hydrophobic as a result of the storagedescribed. Possibly, polar (i.e. hydrophilic) functional groups whichare still contained In the melamine/formaldehyde polymer are eliminatedat the storage temperature of above 180° C., with the result that thepolymer becomes more nonpolar, i.e. more hydrophobic. If a water drop isapplied to such a hydrophobic foam, it retains its hemispherical shapeon the foam surface and is not Immediately absorbed, as in the case ofhydrophilic foam.

The shaped articles can be used as such, i.e. with untreated, inparticular unlaminated, surfaces. In a preferred embodiment, one or moresurfaces of the shaped article have been provided with or laminated withtop layers, for example with glass fiber or textile layers (inparticular nonwovens or woven fabrics), metal sheets, woven metalfabrics or metal foils, plastics layers, woven plastics fabrics,plastics nonwovens or plastics films, which may also be foamed. Textilelayers which may be used are nonwovens or woven fabrics based on glassfibers, polyester fibers, carbon fibers, aramid fibers orflame-retardant natural fibers.

The top layer or lamination can be applied to the surface of the shapedarticle in a conventional manner, for example by adhesive bonding usingadhesives suitable for this purpose, and, particularly in the case ofnonwovens and woven fabrics, also by sewing, quilting, stapling,needle-felting or riveting.

The top layer or lamination can subsequently be applied to the finishedshaped article or, preferably, can be applied during the producton ofthe shaped article. For example, during molding of the foam in step c),the foam can be covered with corresponding top layers or laminations andthen molded, or the top layers or laminations can be placed in thecompression mold and molded with the foam. If it is intended, forexample, to laminate a sheet-like shaped article with a nonwoven A onits underside and with a nonwoven B on its top, the layers can bearranged in the sequence A-S-B and then molded (S=foam layer), with theresult that the shaped article laminated on both sides forms in oneoperation.

Multilayer laminations are of course also possible, for example bysuccessive application of further layers to the finished shaped article,or during the production of the shaped article by molding layers lyingone on top of the other, which were arranged beforehand in the desiredsequence. Of course, a first lamination can be applied during moldingand an additional lamination subsequently.

Particularly preferably, one or more surfaces of the shaped article arelaminated with a hydrophobic or oleophobic textile layer. For example,glass fibers, polyester fibers or polyamide fibers which have beenrendered hydrophobic with paraffin emulsions, silicone emulsions orfluoroalkane emulsions are suitable as the hydrophobic textile layer.For example, glass fibers, polyester fibers or polyamide fibers whichhave been rendered oleophobic with fluoroalkane emulsions are suitableas the oleophobic textile layer.

According to the above description, the invention relates not only tothe shaped articles but also to the process for the production of shapedarticles, comprising the following steps:

-   a) a foam is prepared from a melamine/formaldehyde precondensate    having a molar melamine: formaldehyde ratio greater than 0.5,-   b) the foam obtained is annealed at below 200° C., and-   c) the annealed foam is molded in a press at from 160 to 240° C. and    an absolute pressure of from 5 to 100 bar in the course of from 15    to 120 seconds to give the shaped article;    and it relates to said process, comprising, after the molding (step    c))-   d) storing the shaped articles at above 180° C. for at least 30    minutes.

The novel shaped articles have a wide range of uses. The use of theshaped articles for acoustic or thermal insulation is preferred and islikewise a subject of the invention.

They are used, for example, in the building trade as heat insulation andfor sound insulation of buildings and parts of buildings, in particularof ceilings and walls; and furthermore for heat insulation and soundinsulation of the interiors of vehicles and aircraft, for soundinsulation of vehicle engine spaces and for low-temperature Insulation,for example of cold rooms and liquefied gas containers. Owing to thegreat hardness of crosslinked melamine resins, the shaped articles canalso be cleaning, grinding and polishing sponges having a slightlyabrasive effect, It being possible to apply suitable cleaning, grindingand polishing materials to the surface of the sponge or to introducesaid materials into the interior of the sponge. Furthermore, the spongescan also be rendered hydrophobic and oleophobic for special cleaningtasks.

The use in vehicle construction, in mechanical engineering, in thebuilding trade and for insulating pipelines is particularly preferred.In vehicle construction, the shaped articles are used, for example, asengine hood insulation, dashboard insulation or gear tunnel covering. Inmechanical engineering, they may be employed, for example in combinationwith layers of heavy materials, for sound Insulation of loud engines.These uses are also a subject of the invention

The novel shaped articles have very low formaldehyde emissions. They canbe produced in a simple manner. The finished shaped article exhibits agood impression of the geometry of the compression mold, i.e. it has thedesired geometry, and possesses precise, closed, stable and mechanicallystrong borders or edges.

The novel process for the production of the shaped articles comprises afew simple operations. Thus, no water or steam is required for shaping.Likewise, no binder need be present, in particular there is no need forimpregnation with a binder in an additional operation.

EXAMPLES Novel Example 1

A foam was prepared in a conventional manner from amelamine/formaldehyde precondensate having a molar melamine formaldehyderatio of 0.625 (i.e. 1:1.6) and was annealed at 160° C. with hot air.The annealed foam was cut into 25 mm thick sheets.

The blank was covered on its top and underside in each case with ahydrophobic textile nonwoven. Thereafter, molding was carried out in acontour mold for 30 seconds at a press temperature of 200° C. and apress pressure of 60 bar (absolute).

The shaped article removed from the compression mold exhibited a verygood Impression of the geometry of the compression mold, with stable,closed and mechanically strong lips. The formaldehyde emission was 0.02ppm, measured according to DIN 55666.

Comparative Example 1

Example 1 was repeated, the molar melamine: formaldehyde ratio of theprecondensate being 0.333 (i.e. 1:3) and the foam being annealed at 240°C.

The shaped article removed from the compression mold exhibited anincomplete impression of the geometry of the compression mold, with lipswhich were not closed, and was therefore unusable. The formaldehydeemission was 0.03 ppm, measured according to DIN 55666.

The comparative example shows that shaped articles having a lowformaldehyde content can also be produced from formaldehyde-richmelamine resins. However, a high temperature of 240° C., not accordingto the invention, was required for this purpose. The shaped articleobtained was waste since it was Incorrectly shaped and had inadequateborders.

Comparative Example 2

Example 1 was repeated, the molar melamine: formaldehyde ratio of theprecondensate being 0.333 (i.e.1:3) and the foam was annealed at 160° C.as in example 1.

The shaped article removed from the compression mold exhibited a verygood impression of the geometry of the compression mold, with stable,closed and mechanically strong lips. The formaldehyde emission was 7ppm, measured according to DIN 55666.

When the annealing temperature was reduced, according to the invention,below 200° C., in this case to 160° C., a correctly shaped articlehaving good borders was obtained, but the shaped article did not have alow formaldehyde content: the formaldehyde emission of 7 ppm was muchhigher than the maximum value of 0.1 ppm according to the invention.

1. A shaped article of melamine/formaldehyde foam, which shaped articlehas a formaldehyde emission of less than 0.1 ppm, determined accordingto DIN 55666, and is obtainable by the following process: a) a foam isprepared from a melamine/formaldehyde precondensate having a molarmelamine: formaldehyde ratio greater than 0.5, b) the foam obtained isannealed at below 200° C., and c) the annealed foam is molded in a pressat from 160 to 240° C. and an absolute pressure of from 5 to 100 bar inthe course of from 15 to 120 seconds to give the shaped article.
 2. Ashaped article as claimed in claim 1, which, after the molding (step c),3. A shaped article as claimed in claim 1, wherein one or more surfacesof the shaped article are laminated with a hydrophobic or oleophobictextile layer.
 4. A process for the production of a shaped article ofmelamine/formaldehyde foam, comprising the following steps: a) a foam isprepared from a melamine/formaldehyde precondensate having a molarmelamine:formaldehyde ratio greater than 0.5, b) the foam obtained isannealed at below 200° C., and c) the annealed foam is molded in a pressat from 160 to 240° C. and an absolute pressure of from 5 to 100 bar inthe course of from 15 to 120 seconds to give the shaped article.
 5. Aprocess as claimed in claim 4, wherein, after the molding (step c), d)the shaped article is stored at above 180° C. for at least 30 minutes.6. A melamine/formaldehyde foam having a formaldehyde emission of lessthan 0.1 ppm, obtainable from melamine/formaldehyde precondensate havinga molar melamine: formaldehyde ratio of greater than 0.5 and subsequentannealing at a temperature of below 200° C.